This invention relates to a method of setting the output of a circulating pump which is driven by an rpm-variable electromotor and which is installed in a hot water heating system. The pump is utilized to pump water from a water heater through consumer apparatus situated in different rooms served by the heating system and to return the water through a return pipe to the water heater. At a designated location of the pipe system a measuring device is mounted which determines the flow velocity of the water and which emits an electric signal that is proportionate to the flow velocity. The electric signal is then transmitted to a regulator associated with the electric motor that drives the pump whereupon the regulator varies the rpm of the electromotor dependent upon the signal obtained from the measuring device. A system of this type is disclosed, for example, in German Offenlegungsschrift (Non-examined Published Application) No. 3,508,049.
Heating systems are available in a great number of sizes. They are installed, for example, in single family homes, in rental buildings, in large office buildings or in multi-building complexes. The required pump output to service a particular system is directly dependent upon the size of the heating system. The size is determined essentially by the number of consumer apparatus employed in the system. Thus, in many instances a single circulating pump suffices. In larger installations there is one main pump and additional pumps provided for the individual heating circuits. The maximum output of the pump of a particular heating system is determined by that rate required to sufficiently supply all consumers in that system, when all consumers are requiring a maximum amount of heating medium. It will be understood that by "consumer apparatus" it is meant, for example, heating bodies, flat heaters, heat exchangers or the like.
A full pump output is needed only when all consumer apparatus or at least a significant part thereof, are receiving the fluid medium. In periods--for example, at night or in warmer seasons--where only one part of the consumer apparatus is active, the pump output may be reduced. This also applies to situations when the requirement of consumer apparatus is, for example, throttled by thermostatic valves. If the pump continues its delivery in such cases with full output, it may cause flow noises in the pipe system. Further, in this instance the pump unnecessarily consumes the maximum energy which involves waste and unnecessary costs.
There are therefore commercially available circulating pumps whose electromotor may be driven in stages at different rpm's. The switching from one rpm to another may be effected by appropriate switches either manually or automatically by means of a timer such as a timing clock. In both instances the switchover is effected in a time-dependent manner, based on test data. An adaptation to the actually required output is not feasible with such prior art arrangement. Thus, in such prior art methods or installations it cannot be determined at what time, during the peak load periods, a larger number of consumer apparatus are switched off or at what time, during the period of reduced pump output, a greater number of consumer apparatus are switched on. Particularly, the latter situation may have the adverse effect that the heat requirement as a whole cannot be satisfied.
With the process disclosed in the German Offenlegungsshrift No. 3,508,049 there may be ensured an automatic adaptation of the pump output to the momentary operational conditions. In the process disclosed in this patent the pump output is varied as a function of the flow velocity of the water in the return pipe. For driving the circulation pump an electromotor is used which can be switched over to at least two different rpm's in a stewise manner. Such a process has been found workable in practice. However, the switchover operation to the different rpm stages requires a relatively complex switching system and furthermore, in the above-mentioned method, a continuous adaptation of the pump output of the circulating pump is not possible.